Decrease in anthropogenic nutrients and its effect on the C/N/P molar ratio of suspended particulate matter in hypertrophic Dokai Bay (Japan) in summer |
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| Authors: | Kenichiro Hamada Naoko Ueda Machiko Yamada Kuninao Tada Shigeru Montani |
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| Institution: | (1) Aqua Research Center, University of Kitakyushu, Hibikino 1-1, Wakamatsu-ku, Kitakyushu 808-0135, Japan;(2) Faculty of Human Environment Science, Fukuoka Women’s University, Kasumigaoka 1-1-1, Higashi-ku, Fukuoka 813-8529, Japan;(3) Faculty of Agriculture, Kagawa University, Ikenobe, Mikicho, Kita-gun, Kagawa 761-0130, Japan;(4) Graduate School of Environmental Science, Hokkaido University, Kita 10, Nishi 5, Kita-ku, Sapporo 060-0810, Japan;(5) Present address: Fisheries Section, Agriculture, Forestry and Fisheries Department, City of Kitakyushu, Jyounai 1-1, Kokurakita-ku, Kitakyushu 803-8501, Japan |
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| Abstract: | Biologically important nutrient concentrations in Dokai Bay have declined as a result of reductions in anthropogenic inputs
of total nitrogen and total phosphorus. A decrease in nutrient concentrations affects phytoplankton growth, thereby changing
the biochemical characteristics of autochthonous particulate matter. We therefore investigated changes in the C/N/P molar
ratio of suspended particulate matter (SPM) in the summer, when phytoplankton growth is vigorous, before environmental quality
standards (EQSs) were attained (1995–1998) and afterward (2006–2009). We found that the ratio of particulate organic nitrogen
(PON) to particulate phosphorus (PP) changed in conjunction with changes in the ratio of dissolved inorganic nitrogen to dissolved
inorganic phosphorus (DIP) that resulted from reductions in nutrient loading. Furthermore, we suggest that because the DIP
concentration in seawater was high before EQSs were attained, inorganic phosphorus was possibly adsorbed onto SPM. After the
attainment of EQSs, however, the DIP concentration fell, and PON/PP was high. Phosphorus limitation of phytoplankton growth
in the mouth of the bay may explain the high PON/PP ratios after EQS attainment. |
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